They just have to keep recruiting more people, so the long term survival would be predicated on the expectation that they won't ever recruit enough to starve their own supply. If they did reach that point, they'd probably change their policies.

But I don't think grifters care about the long term anyway. If they can make enough bank in the short term, they don't need to develop a sustainable strategy for what happens if their cash cow eventually hits the growth limit or starts reversing.